1. Technical Field of the Invention
This invention relates to acoustic musical stringed instruments and more particularly to a novel soundboard bracing structure system for improving the quality of the musical sound that is produced by such instruments.
2. Description of Prior Art
Musical stringed instruments such as acoustic—steel or nylon stringed guitars, lutes and the like are typically comprised of a neck attached to a hollow body. The body usually consists of a top face, termed the sound board, to which side walls are formed and attached around its perimeter, the side walls also attach to a backboard, enclosing an air filled chamber. The air filled chamber also referred to as a resonator, can vary in size, shape or form. Traditionally constructed from different timber species but also in recent times using modern materials such as polyester glass reinforced resin or even carbon composites.
The soundboard usually has one or more openings referred to as a “soundhole”, which can vary in shape and location. A bridge structure is engaged to the soundboard and made large enough to attach a plurality of strings to. The bridge structure can simply be rectangular or some other shaped piece of hard timber or made from other suitable materials. The strings connected to the bridge pass over but make firm contact on to a thin strip of hard material such as bone or brass which is recessed into the bridge and is usually referred to as the bridge “saddle”
The strings continue over the saddle and are stretched to the end of the neck where they pass over but make firm contact onto a notched thick strip of hard material, referred to as a “nut” which is fixed to the neck end of the instrument. The strings are then secured to turn able pegs or machine tuners fixed to a “head” plate at the free end of the neck. The pegs or tuners are used to individually tension the strings to a predetermined pitch producing certain musical notes of frequencies when struck or plucked.
Where vibrating strings make contact with the recessed bridge saddle is where the vibrations of the strings pass through into the soundboard. Sound is generally a wave disturbance of air. The amount of air that can be disturbed by the surface area of a vibrating string alone is fairly negligible compared to the vibrating surface area of the soundboard. Ideally the entire soundboard will vibrate in unison with the vibrating string(s) causing the air inside the hollow body to wave, reflect and to essentially resonate and emanate through the sound hole. Thus amplification of the vibrating string(s) is achieved.
The above is a general simplification in the workings of acoustic musical stringed instruments. In fact there are many factors; forces, parameters, material characteristics to consider.
A close examination of musical stringed instruments shows that the soundboards are generally extremely thin compared to their surface area's and usually made from a soft timber such as spruce or pine. Such soundboards are able to vibrate more freely or vigorously than thicker ones and therefore are able to displace greater volumes of air within the hollow body, essentially producing greater amplification of sound.
Unfortunately the soundboards are not self-supporting and their resistive capabilities towards the tensional forces of the strings are minimal. Hence traditional and modern acoustic musical stringed instruments have braces glued to the underside of the soundboard. There have been many designs and patterns devised trying to produce the best possible outcome in sound-volume and tonal qualities. Designers have tried to use bracing systems to not only support the soundboard but also to spread the vibrations throughout the surface area of the soundboard. For guitars with six strings there are two bracing systems currently used as an industry standard and each may vary slightly from one guitar manufacturer to another. One is an “X” bracing system developed by C.F. Martin & Company in the mid nineteen hundreds and mainly used for larger steel stringed guitars such as the dreadnought; to which the shape and size is also attributed to C.F. Martin & Company. The other is a “FAN” bracing system largely used for smaller body gut or nylon stringed guitars that was developed by Antonio Torres in the mid eighteen hundreds. He is also acclaimed to have designed the present shape and size of the modern “Spanish classical guitar” body.
Soundboard with “X” bracing systems have shortcomings that are deflections and deformities by way of compression and bulging. On observation it can be seen that the area front of the bridge becomes compressed down while the area behind the bridge and extending towards the end block bulges upwardly. Deflections also occur in the areas halfway along the four arms of the “X” bracing, to where smaller braces are often fixed to the soundboard. Further deflection can also be found at the ends of the “X” bracing arms at these points the deflections cannot be noticed visually. The important thing to note is that the side-walls of the body take up some of the string load tension and more importantly the soundboard is placed under stress and is not able to vibrate uniformly due to all the summed up deflections which have been caused by the lack of direct support for the directional load tension of the strings.
“FAN” bracing systems are usually found in nylon stringed classical Spanish type guitars. Fan bracing normally comprises of a substantial brace glued under the soundboard, just below the soundhole and perpendicular to the line of the strings. Effectively the larger portion of the soundboard, from the waists of the body down to the end-block of the body is isolated from the upper part. In the larger portion of the soundboard, several long thin bracing bars are arranged in a fan like pattern generally in the same direction as to the strings and fixed to the underside soundboard surface. A long rectangular bridge glued to the top of the soundboard lies somewhat central and perpendicular to the fan-bracing pattern. The whole function of the fan-bracing pattern is to spread out the vibrations into the soundboard that are coming from the bridge. Even though this type of guitar normally exhibits only about half of the string tension that is found on steel stringed guitars, the same sorts of problems that are found on the “X” bracing system are also apparent in the “FAN” bracing system. Deflections of the soundboard can be noticed in the upper body area, above the main brace and to a greater extent in front and behind the bridge areas of the lower part of the body. All of the deflections and deformities are due to the lack of direct support for the strings directional load tension, exerted onto the soundboard via the bridge.
The “X” and “FAN” bracing systems being used by guitar manufacturers today all tend to restrict the uniform vibrating motion of the soundboard, as discussed above. The main reasons for using these said bracing systems, is so that the soundboard is not overly stiffened, thus allowing the string(s) to vibrate the soundboard strongly.
The strings under load tension exert a force at their two fixed end points, with one end attached to the bridge of the soundboard and the other end attached to the head plate of the neck. In part a rotational torque force is also potentially exerted onto the nodal points being the nut and saddle. The available transmissions of the vibrating string energy that is directed into the soundboard occurs at the nodal point source of the saddle, but the strings vibrating duration period is largely governed by the support structure that holds the strings. The continuation (sustain) of the vibrating string(s) can only occur, if the string(s) are held by a ridged support structure.
However using a ridged support structure to allow for a prolonged string sustain period; and thereby also alleviating the soundboard from the tensional forces of the strings so that it can also vibrate uniformly; is not a new concept nor is it easily achievable. All past attempts have adversely affected the instruments tonal qualities and reduced the transmissions of the vibrating strings, into the soundboard.
In fact many bracing patents have been proposed to address the problem. As far back as the early nineteen hundreds, patents have been submitted where the entire neck is extended through the hollow body and firmly fixed to the end-block of the body, as may be seen in US patents such as; U.S. Pat. Nos. 1,754,263; 1,426,852; 1,889,408; 2,793,556 and more recently U.S. Pat. No. 5,679,910. Some models incorporated a solid beam, or one or two steel rod(s) fixed 125 between the neck heal-block and the end-block of the body, with a screw-out jack in the middle of the rod(s) or at the end-block location; in an effort to pre-tension and thereby relieve the soundboard, from the tensional forces of the strings.
The use of through rod type systems puts stress on the soundboard. Central flexing of the rods occurs and is at odds with the vibrating soundboard, putting the soundboard under a damping effect, due to opposing tensions. This damping effect cuts short the natural harmonic frequencies produced by the strings and therefore buffers the natural qualities of the sound.
Other attempts to support the string tension by locating the through body neck-beam-section closer to the soundboard still have the same problems, even when longitudinal and transverse bracing has been used under the soundboard.
Other patents like U.S. Pat. No. 5,025,695 propose that a through body neck beam be glued to the soundboard and have it ending at the bridge area. This requires the soundhole to be located away from the line of the neck. Alternatively the paten proposes to simply affix two or more brace bar supports by gluing them directly under the sound board, where the through body neck beam would normally come through and also ending at the bridge area. Alternatively the through body neck beam is clear of the soundboard but ending at and glued to an area under the bridge.
Consequently most of the strings vibrations are upheld within the strings and in part transmitted into the ridged support structure upholding the strings tension, rather than diverting it into the soundboard, were it would be most useful.
It's clear that vibrating string energy is not easily transmitted into the soundboard, whilst trying to support the tensional forces of the string(s), using the above bracing structures and or bracing pattern systems discussed.
It's also clear that the soundboard is not able to vibrate uniformly due to unwanted soundboard deflections. Since whether the deflected areas are large small or differ in magnitude, they are areas under stress or strain and because of this fact, they will resist and deform the oncoming vibrations through the soundboard.
The soundboard can be considered to be a thin membrane. The unified motion of a thin membrane is one in which the central area of the membrane waves up and down (perpendicular to its surface area), traveling at an equal distance from its central position in every direction outwardly towards its perimeter. In doing so the membrane also displaces the air above it and below it uniformly, propagating air-sound waves in the truest possible form, but only if it is in a stress free state to begin with.
3. A General Description for the Content of Musical Tones or Notes.
The structure of musical tones or notes is a known science that explains the behavior of sound waves to create a harmonious sound.
Generally a musical note produced by a vibrating string is made up of several pure sine wave harmonics, along with its fundamental sine wave frequency, (f1). Basically the harmonics are multiples of the fundamental i.e. 2×f1, 3×f1, 4×f1 etc, increasing in frequency but unfortunately decreasing rapidly in amplitude (sound level).
The first few harmonics produced are what makes the musical note sound musical, the more these harmonics can be heard, the richer and fuller the sound becomes.
An acoustic musical stringed instrument that can produce high values of acoustic sound intensity (volume amplitude) has a desirable quality, but the sound intensity of the harmonics that are produced by the action of the vibrating strings are generally of greater importance to the musical notes, as can be seen from the above statement.
When playing several notes of a melody, the duration of a musical note within the melody may also need to be sustained. With a rapid loss in harmonic sound levels this is not easily achievable. The musical note can be dramatically reduced to what is commonly referred to as a “dead note”.
The musician can struggle with the dead note by using a technique called vibrato, where the string is depressed harder and vibrated more so by the rocking motion of the finger. This vibrato action produces more of a wavering sound, rather than a long lasting continuous sound which is more correctly the sustain that's wanted.
From the above information it's understood that while a high value of acoustic sound intensity is desirable, the sound intensity of the harmonics along with sustained harmonic sound levels is more important to the content and production of musical notes.
Without sustain of sound volume levels and the presence of high sound volume levels for the harmonic content of musical notes, the quality factor of a full rich sound is not produced.
To produce an equal sustain period within a range of strings, say for the six strings of a commonly produced guitar today, is not achievable.
When we consider the unit per length of mass weight, is greatly different from a bass string to a treble string. It is this mass weight of the individual string that governs how long a period it will vibrate for. With all six strings held by the same support structure, typically the bass strings will sustain longer than the treble strings.
Putting initial volume levels aside, the restricted condition of sustain between the individual strings of the range of strings fortunately does not have to be a huge problem. When its considered that an individual note produced by a high frequency treble string, would not normally need to be sustained for more than a full note period in the passage of a 4/4 bar in the musical score. Just the same though, even sustain of this short period of time would rarely be found in the high treble range of industry standard guitars produced today.
Collectively several musical notes sounded together from a plurality of strings must also have equal sound levels (be balanced). This is so they do not mask or obscure each other's musical potential.
The features describing “string range balance” are: initial equal sound levels between all strings, a period of sustained sound levels that is manageable between strings and clear clean sound with harmonic content for all musical tones or notes. An acoustic musical stringed instrument with these qualities could be described as, a well-balanced instrument.
For example a six stringed guitar typically produced today having a bass to treble range extending 3 octaves, have a loud ringing bass with diminished trebles so their string range is musically restricted.
Today a musician is able to choose an acoustic musical stringed instrument such as a guitar produced by large industry manufactures. The musicians will trial the instruments empirically with a view simply tending towards a mellow tone, warm tone or a bright tone.
Different species of timbers used for the soundboard are able to produce various tones by their own characteristics and will influence the musician's choice, such as the warm tones produced by cedar and the bright tones produced by spruce.
The nylon or gut strings of a classical guitar will produce a mellow tone, and in conjunction with either a cedar or spruce soundboard will have a warmer or brighter mellow tone.
Looking for other more important qualities such as a well-balanced string range response; the musician invariably will then experiment with a large assortment of strings made from different materials and thereby producing differing tonal qualities, and according to the string(s) diameter or density will also produce varying periods of sustain when vibrated. Usually the experiments result into an unacceptable or restricted outcome.
In my business over the past thirty years of repairing and servicing acoustic musical stringed Instruments I have often heard musicians complaining about the “string range balance”, using remarks such as; “sounds too tin-y, no middle, overly bass-y, no sustain, lots of dead notes, not clean, dirty” or “muddy and cloudy”.
The novel bracing structure system of the invention that I will be describing to follow enhances the playing experience for the musician and listener alike, as the above problems are substantially alleviated.